Ensure consistent sort direction when listing issues, PRs

The default direction when sorting by `created` date (the default) is
descending. However, the default on the API backend changes to ascending
when the sort key is something different than `created`:
https://developer.github.com/v3/pulls/#list-pull-requests

This ensures that the default `direction: "desc"` is always passed to
API queries, regardless of the sort key, unless `--sort-ascending` was used.

Ref. https://github.com/github/hub/issues/1815#issuecomment-433222344

commands/issue.go

@@ -248,6 +248,8 @@ func listIssues(cmd *Command, args *Args) {
 
 		if flagIssueSortAscending {
 			filters["direction"] = "asc"
+		} else {
+			filters["direction"] = "desc"
 		}
 
 		if cmd.FlagPassed("since") {

commands/pr.go

@@ -182,6 +182,8 @@ func listPulls(cmd *Command, args *Args) {
 	}
 	if flagPullRequestSortAscending {
 		filters["direction"] = "asc"
+	} else {
+		filters["direction"] = "desc"
 	}
 
 	pulls, err := gh.FetchPullRequests(project, filters, flagPullRequestLimit, nil)

features/issue.feature

@@ -9,7 +9,7 @@ Feature: hub issue
     get('/repos/github/hub/issues') {
       assert :assignee => "Cornwe19",
              :sort => nil,
-             :direction => nil
+             :direction => "desc"
 
       json [
         { :number => 999,
@@ -76,7 +76,7 @@ Feature: hub issue
     get('/repos/github/hub/issues') {
       assert :assignee => "Cornwe19",
              :sort => nil,
-             :direction => nil
+             :direction => "desc"
 
       json [
         { :number => 999,

features/pr-list.feature

@@ -10,7 +10,7 @@ Feature: hub pr list
       assert :per_page => "100",
              :page => :no,
              :sort => nil,
-             :direction => nil
+             :direction => "desc"
 
       response.headers["Link"] = %(<https://api.github.com/repositories/12345?per_page=100&page=2>; rel="next")